In semiconductor devices that switch high current, connections between element electrodes of semiconductor elements and external electrodes need to be suitable for the high current. In a case where solid-phase bonding by a wire bonding method is used for the connection, a plurality of metal wires that are made of aluminum or the like and have a large wire diameter are wire-bonded in parallel. To handle higher current and higher voltage, measures of increasing the number of metal wires connected in parallel or increasing the wire diameter of the metal wires need to be taken. The measures being taken increase a necessary electrode area for bonding, thereby increasing a size of the semiconductor device. Moreover, the measures have been more difficult to be taken in terms of a structure and mounting. Thus, technologies except for the wire bonding method have been developed.
Japanese Patent Application Laid-Open No. 2008-182074 (Patent Document 1) discloses that an external electrode being a copper plate is directly bonded to an element electrode of a semiconductor element with solder. This can achieve a connection capable of reducing electrical resistance and passing high current.
Japanese Patent Application Laid-Open No. 2010-272711 (Patent Document 2) discloses that an Ni layer having an appropriate thickness is formed as a metal film for solder bonding to improve reliability in the solder bonding. The optimization of the thickness of Ni can combine process feasibility with bonding reliability more sufficiently.